1. Field of the Invention
The present invention relates to ink jet printing apparatus, and more particularly, to method and apparatus for starting and stopping the flow of ink from a plurality of orifices onto a printing media.
2. Prior Art
At start-up and shut-down of ink jet printing devices a problem exists with how to keep the initial and terminal flow from the streams of ink issuing from the orifices from impacting on the media. At start-up and shut-down of the devices, the system is not immediately active and drops are not being charged and deflected to form the desired patterns until the system has reached a steady state with the flow of ink from all of the orifices being consistent.
Several devices have been developed which attempt to stop the flow of ink in the reservoir and thus prevent any ink from issuing from the orifices. However, this requires precise and expensive valving arrangements and shaping of the reservoir and orifice accordingly to prevent the dripping of ink after the valves have been shut off.
Still other apparatus have been developed which mechanically close off the orifices by passing a gate or other physical structure in front of the orifices to close them off. However, by passing the gate through the streams of ink issuing from the orifices, the leading edge of the gate causes a splattering of ink which is undesirable.